U.S. patent number 3,983,793 [Application Number 05/638,637] was granted by the patent office on 1976-10-05 for crosshead piston assembly.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to John M. Beardmore.
United States Patent |
3,983,793 |
Beardmore |
October 5, 1976 |
Crosshead piston assembly
Abstract
An internal combustion engine crosshead piston assembly having
an outer skirt mounted by an elastomeric member on an inner skirt
to reduce piston-slap-caused noise wherein expansible chambers are
provided in the elastomeric member and are connected by orifices in
the inner skirt to receive and eject oil to provide cooling of the
outer skirt and also add a damping effect to further reduce the
noise.
Inventors: |
Beardmore; John M. (South Lyon,
MI) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
24560840 |
Appl.
No.: |
05/638,637 |
Filed: |
December 8, 1975 |
Current U.S.
Class: |
92/190; 92/195;
92/126; 92/212 |
Current CPC
Class: |
F16J
1/02 (20130101); F16J 1/04 (20130101); F16J
1/14 (20130101); F05C 2201/021 (20130101) |
Current International
Class: |
F16J
1/02 (20060101); F16J 1/04 (20060101); F16J
1/14 (20060101); F16J 1/10 (20060101); F16J
1/00 (20060101); F16J 001/02 (); F16J 001/04 ();
F16J 001/14 () |
Field of
Search: |
;92/215,187,212,195,190,126,214,193,208,249 ;123/193P |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Cohen; Irwin C.
Attorney, Agent or Firm: Phillips; Ronald L.
Claims
I claim:
1. An internal combustion engine crosshead piston assembly
comprising a head member, a cylindrical inner skirt member, a
piston pin for pivotally connecting both said head member and said
inner skirt member to a piston rod while permitting relatively
small angular movement between these members, said inner skirt
member having an outer annular recess, a cylindrical outer skirt
member arranged in said recess, a cylindrical elastomeric member
arranged in said recess between said skirt members, said
elastomeric member having an inner side bonded to said inner skirt
member and an outer side bonded to said outer skirt member, said
elastomeric member further having longitudinally extending
expansible chambers that change in volume with changing radial
thrust loads, flow restricting passages in said inner skirt member
connecting each said chamber at longitudinally spaced points to the
interior of said inner skirt member, and said outer skirt member
extending substantially radially outwardly of both said head member
and said inner skirt member whereby said elastomeric member is
effective to both distribute and transmit any radial thrust loads
acting on said inner skirt member to said outer skirt member with a
relatively low spring rate and relatively high energy absorption
factor to thereby reduce piston-slap-caused noise while a portion
of any oil splashing within the piston assembly is circulated
through said chambers to cool said outer skirt member and also add
a damping effect on chamber contraction to further reduce
piston-slap-caused noise.
2. An internal combustion engine crosshead piston assembly
comprising a head member, a cylindrical inner skirt member, a
piston pin for pivotally connecting both said head member and said
inner skirt member to a piston rod while permitting relatively
small angular movement between these members, said inner skirt
member having an outer annular recess, a cylindrical outer skirt
member arranged in said recess, a cylindrical elastomeric member
arranged in said recess between said skirt members, said
elastomeric member having an inner side bonded to said inner skirt
member and an outer side bonded to said outer skirt member, said
elastomeric member further having longitudinally extending
expansible chambers that change in volume with changing radial
thrust loads, a large and a small orifice in said inner skirt
member connecting each said chamber adjacent the respective upper
and lower ends thereof to the interior of said inner skirt member,
and said outer skirt member extending substantially radially
outwardly of both said head member and said inner skirt member
whereby said elastomeric member is effective to both distribute and
transmit any radial thrust loads acting on said inner skirt member
to said outer skirt member with a relatively low spring rate and
relatively high energy absorption factor to thereby reduce
piston-slap-caused noise while a portion of any oil splashing
within the piston assembly is circulated through said chambers to
cool said outer skirt member and also add a damping effect on
chamber contraction to further reduce piston-slap-caused noise.
Description
This invention relates to an internal combustion engine crosshead
piston assembly and more particularly to such an assembly wherein
the piston thrust stiffness is reduced by an elastomeric
arrangement to effect reduction in piston-slap-caused noise while
very efficient cooling is maintained.
It has been found that in certain internal combustion engines, such
as two-cycle diesel engines, that the most significant mechanical
noise source within the engine structure is that caused by piston
slap. Thus, a significant noise reduction in such a total engine
package could be effected by first reducing or lowering the piston
slap noise. In this environment there are several important
parameters to consider; namely, piston-to-liner clearance,
piston-to-liner motion damping, piston mass and piston thrust
stiffness. This assumes no changes in combustion characteristics
(namely peak pressure) or engine speed.
Of these parameters, a reduction in the piston thrust stiffness
would be particularly effective if it was possible to somehow
provide a relatively low rate spring in the skirt structure. In
most piston designs, however, the skirt is also required to act as
a heat transfer medium between the piston and liner and as a result
there is imposed an unsatisfactory limit on reduction in skirt
stiffness from a noise standpoint but it was found that in certain
crosshead piston designs this is not the case. For example, in the
crosshead piston disclosed in U.S. Pat. No. 3,555,972 assigned to
the assignee of this invention, actual temperature measurements
have shown that good piston cooling can be effectively accomplished
by the forced feeding of lubricating oil with resulting skirt
temperatures only slightly above the oil sump temperature. The
present invention takes advantage of the structural and temperature
characteristics of crosshead piston assemblies of this type to
provide a very simple arrangement with a substantially reduced
thrust stiffness brought about by a built-in relatively low spring
rate, support-hydraulic energy absorber for the skirt that is
effective to reduce the piston slap noise without substantially
increasing the lowered skirt temperature.
In the crosshead piston assembly of the present invention, there is
a cylindrical head member of relatively high strength material and
a cylindrical inner skirt member of relatively light weight
material which are independently pivotally connected by a piston
pin to a piston rod, there being slight angular movement permitted
between the head and inner skirt. The inner skirt is provided with
an outer annular recess in which a cylindrical relatively thin wall
outer skirt member having an outer surface of relatively high wear
resistant material is mounted with limited relative axial movement.
A cylindrical elastomeric member is arranged in the recess between
the two skirt members and is bonded on opposite sides to these
members. The outer skirt member extends substantially radially
outward of the head member and the inner skirt member to contact
with the cylinder wall and the elastomeric member is effective to
both distribute and transmit any radial thrust loads acting on the
inner skirt member to the outer skirt member with a relatively low
spring rate and relatively high energy absorption to thereby reduce
piston-slap-caused noise. In addition, the elastomeric member is
provided with longitudinally extending expansible chambers that are
connected by orifices in the inner skirt to receive oil from and
eject oil to the piston interior to provide cooling of the outer
skirt and also add a damping effect to further reduce the
noise.
An object of the present invention is to provide a new and improved
crosshead piston assembly.
Another object is to provide an improved internal combustion engine
crosshead piston assembly having an elastomerically mounted skirt
that reduces piston-slap-caused noise without substantially
increasing skirt temperature.
Another object is to provide in an internal combustion engine
crosshead piston assembly an outer skirt mounted on an inner skirt
by an elastomeric member with expansible oil chambers that is
effective to both distribute and transmit any radial thrust loads
acting on the inner skirt to the outer skirt with a relatively low
spring rate and relatively high energy absorption to thereby reduce
piston-slap-caused noise while oil circulating through the chambers
via orifices in the inner skirt cools the outer skirt and also
provides a damping effect to further reduce the noise .
These and other objects of the present invention will be more
apparent from the following description and drawing in which:
FIG. 1 is a longitudinal sectional view of a piston and connecting
rod assembly embodying the present invention.
FIG. 2 is a view taken along the line 2--2 in FIG. 1.
FIG. 3 is a view taken along the line 3--3 in FIG. 1.
FIG. 4 is an enlarged view taken along the line 4--4 in FIG. 1.
FIG. 5 is a perspective view of the piston and connecting rod
assembly.
A preferred embodiment of the present invention is disclosed in
detail in a piston and rod assembly generally designated as 10 for
use in current high output engines, especially diesel engines. As
best shown in FIGS. 1 and 2, the assembly 10 includes a connecting
rod 12, the lower portion of which has been deleted to simplify the
drawing, a piston pin 14 and a piston assembly 16. The piston
assembly includes two primary elements--a head membeer 18 and a
skirt, or crosshead assembly 20.
The piston head member includes a crown section 22 extending over
the upper surface and forming a combustion chamber defining wall.
Depending from the outer edge of the crown section is an outer
annular ring belt section 23 in which are formed three compression
ring grooves including a top, or fire, ring groove 24 at the
juncture of the crown and ring belt sections and second and third
compression ring grooves 26 and 27 respectively located in a lower
part of the ring belt section and separated from the top ring
groove 24 by a thinner walled heat dam portion 28. Below the third
ring groove 27, the ring belt section terminates in a reduced
diameter portion 30 which includes a seal ring groove 32.
The piston head member further includes a piston pin connecting
section 33 generally comprising a pair of spaced, downwardly
extending, pin encircling arms 34 interconnected at their upper
ends by a saddle portion 36 which is in turn connected with the
crown section by a plurality of axially and radially extending
struts or columns 37. Columns 37 include radially outwardly
extending rib portions 38 integrally connecting them with the ring
belt section and with the outer portions of the crown section.
Saddle portion 36 defines a downwardly opening part-cylindrical
recess 40 coaxially aligned transversely of the piston axis with a
pair of piston pin receiving openings 42 formed in pin encircling
arms 34. Recess 40 terminates circumferentially in a pair of radial
shoulders 43 which are adapted to retain in the recess a
part-cylindrical bearing insert 44 having an inwardly facing
bearing surface preferably containing a plurality of grooves (not
shown) for the distribution of lubricant thereover. A retainer tang
(not shown) at one edge of insert 44 is deformably received in a
recess of the saddle portion to retain the insert from movement
along its axis after installation. Between arms 34 and adjacent
recess 40 the saddle portion is flared outwardly as at 48 and
terminates in a depending rim 50. Oil drain openings 52 are drilled
vertically through the outwardly flared portions 48. At the lower
ends of arms 34, excess material 53 is provided which may be
removed as desired in order to obtain the proper weight and balance
of assembly. Cooling oil supply openings 54 and 55 are provided in
the centers of the saddle portion and bearing insert respectively,
the latter also having an arcuate recess 56 in its inner surface
connecting with opening 55 and with oil distribution grooves (not
shown) extending over the bearing surface.
The crosshead or skirt assembly 20 includes a cylindrical skirt
member 57 having cylindrical pin receiving openings 60 which, when
the head member and skirt unit are assembled, are coaxially aligned
with the pin encircling openings 42 of the head member pin
connecting section. Between the openings 60 interior of the skirt
there are provided circumferentially and radially inwardly
extending ribs 62. Shallow counterbores 63 are provided near the
outer ends of the pin receiving openings 60 to receive metal
closure plates 64.
At its upper end, the skirt 57 is counterbored to form an annular
shoulder or wall portion 66 which, in assembly, surrounds the
reduced diameter portion 30 of the head member ring belt section. A
relatively small clearance is provided between them and this is
sealed by suitable means such as a metal seal ring 67 which
includes overlapping ends to close the end gap. The seal ring is
received in the ring groove 32 of the head member and is expanded
by a conventional spring piston ring expander 68.
At its lower end, skirt 57 has two oil ring grooves 72 to provide
for receiving suitable oil scraper rings to control the amount of
oil on the engine cylinder walls. Below each groove 72 are a
plurality of oil drain holes 73 to carry oil away from the oil
rings in a conventional manner.
The head and skirt of the piston assembly are retained together by
the cylindrical piston pin 14 which is received in openings 60, 42
of the skirt and head members respectively and engages, across a
substantial portion of the pin's upper surface, the bearing insert
44 retained within recess 40. Piston pin 14 is hollow and has
oppositely disposed upper and lower radial openings 76 and 77
respectively. On opposite sides of lower opening 77, a pair of bolt
clearance openings 78 are also provided.
The piston pin 14 is secured against the saddle portion 80 of the
connecting rod 12 by bolts 83 which extend through openings 84 in
the rod and openings 78 in the piston pin into engagement with
threaded openings 85 in an elongated nut 86 disposed within the
piston pin 14. If desired, the connecting rod and nut may be
arranged in a known manner so as to prestress the pin by deforming
it into an oval shape in its unloaded condition. Nut 86 also
includes a central opening 87 which is aligned with openings 76 and
77 of the pin and together with them receives a tube member 88 for
the purpose of providing a transverse oil passage through the pin.
In assembly, the passage formed by tube 88 aligns with a drilled
passage 90 extending lengthwise through the connecting rod 12.
In typical piston operation, oil is supplied from the engine
lubricating oil system through a drilled passage 90 in the
connecting rod and tube 88 in the piston pin to recess 56 of the
bearing insert, from which part of the oil is distributed over the
surface of the insert through the distributing grooves (not shown)
for lubricating the bearing surface. The majority of the oil
supplied continues upward through openings 55 and 54 of the bearing
insert and piston head saddle respectively and enters the
undercrown cavity of the piston in which it is sloshed against the
underside of the crown by the reciprocating motion of the piston.
This action provides cooling of the crown, ring belt and connecting
columnar ribs of the piston head structure. The oil is prevented
from freely draining out of the undercrown cavity by cooperation of
the saddle portion of the piston head with the ribs 62 of the
piston skirt, the latter of which fit closely around the depending
rim 50 of the outwardly flared part of the saddle portion. Instead,
the drain openings 52 provide for controlled drainage of cooling
oil from the undercrown cavity.
Closure plates 64 prevent leakage of the oil, used to lubricate the
pin, from the ends of the pin receiving openings and onto the
piston skirt. Drain openings (not shown) provide for the return to
the engine crankcase of any oil collecting at ends of the piston
pin.
The structure thus far described is of known type and may have
further details as disclosed in the aforementioned U.S. Pat. No.
3,555,972. In such an assembly it has been found that piston slap
is the most significant mechanical noise source within the engine
structure. Thus, significant noise reductions in the total engine
package could be effected by first reducing the piston slap noise.
One way to reduce piston slap noise is to reduce piston thrust
stiffness which requires building a relatively low spring rate into
the skirt structure. But on most piston designs the skirt acts as a
heat transfer path between the piston and cylinder. However, it has
been found that in the crosshead piston of the above type this is
not the case with actual temperature measurements having shown that
piston cooling is effectively accomplished by forced feeding of the
lubricating oil. For example, it has been found in such piston
assemblies that the resulting skirt temperatures were only about
10.degree. F. above an oil sump temperature of 250.degree. F. or
about 260.degree. F. In some areas the cylinder is hotter than this
and in the case of a turbocharged engine the air going into the
cylinder may be even hotter, for example about 300.degree. F. at
rated power outputs.
The fact that the piston head and skirt are separately connected to
the piston pin permits a small amount of relative motion between
them so that movements of the piston skirt, caused by its natural
motion from side to side in the cylinder as it absorbs the thrust
loads placed upon the piston by oscillation of the connecting rod,
are not transmitted to the piston head portion. Thus, the head
portion is subjected essentially only to the combustion and inertia
forces which act along the axis of the engine cylinder. This
permits the piston head to take a relatively fixed position within
the engine cylinder and avoids unnecessary shifting and wear of the
piston rings within the grooves. The axial combustion and downward
inertia loads are distributed over substantially the entire upper
surface of the piston pin by its contact with the insert bearing
received within the part cylindrical recess of the piston saddle
portion. These features combine to provide a high capacity piston
construction capable of operating under high temperatures with high
loads and providing excellent conditions for extended operation of
the skirt and head portions as well as the piston pin bearing.
According to the present invention an elastomeric outer skirt
mounting arrangement with hydraulic damping is utilized to reduce
noise caused by piston slap against the cylinder resulting from the
thrust loads and without substantially increasing skirt
temperature. This modification comprises providing the normal skirt
57 with a reduced diameter portion 100 which terminates at its
lower end with a radially extending shoulder 102 below the piston
pin receiving openings 60 and terminates at its upper end beneath
the radially extending shoulder 104 of the piston head's ring belt
section 23. The reduced diameter portion 100 with its shoulder 102
cooperates with the piston head shoulder 104 to form a radially
outwardly facing annular recess on the skirt member 57 in which a
cylindrical relatively thin wall outer skirt member 106 is located.
A cylindrical, relatively low spring rate, hydraulic damper member
108 of elastomeric material such as rubber is located in the recess
between the two skirt members 57 and 106 and is bonded on opposite
sides to these members, the outer skirt member 106 and elastomeric
spring member 108 being mounted on what can now be called the inner
skirt member 57 prior to assembly of the latter with the piston
head and piston pin.
The elastomeric spring-hydraulic damper member 108 is provided on
its internal cylindrical surface 110 in the piston's diagonally
opposite thrust regions with axially extending, angularly spaced,
voids or recesses 112 which cooperate with the cylindrical surface
100 of the inner skirt to provide expansible oil chambers 114 which
extend radially outward close to the inner surface of the outer
skirt 106. The chambers 114 terminate near the ends of the
elastomeric member 108 and extend substantially the length of the
outer skirt member 106. The inner skirt member 57 is provided near
the top thereof with relatively large orifices 116 through the
skirt wall. The orifices 116 open at their radially outer end to
the expansible oil chambers 114 near the top thereof while the
inner end of these orifices open to the undercrown cavity of the
piston assembly above the piston pin connecting section 33 in the
region where oil is being force fed via opening 54 in the piston
head saddle 36. In addition, the inner skirt member 57 is provided
near the bottom thereof with relatively small orifices 118 which
extend through the inner skirt wall and open at their radially
outer end to the expansible oil chambers 114 near the bottom
thereof. The radially inner end of the small orifices 118 opens to
the interior of the piston assembly below the piston pin connecting
section 33 and thus to the return path that the oil takes to the
sump. In addition, the outer skirt member 106 and the elastomeric
spring-hydraulic damper member 108 are provided with openings 120
and 122 to leave open the closure plates 64.
The thus elastomerically mounted outer skirt member 106 which may
be either performed and then bonded in place or may be injection
molded in situ and cured, extends substantially radially outwardly
of the piston head's ring belt section 23 and the remaining oil
ring groove portion of the inner skirt member 57 so that it has a
sliding bearing fit in the cylinder that helps to maintain
clearance between the cylinder and both the head member and inner
skirt member. As a result, when there occurs a thrust load, the
elastomeric spring characteristic of the mounting or suspension
member 108 with the displacement allowed by the chambers or voids
114 is effective to both distribute and transmit the thrust loads
from the inner skirt member 57 to the outer skirt member 106 with a
relatively low spring rate and relatively high energy absorption
factor to thereby reduce piston-slap-caused noise. For example, the
allowed motion of the outer skirt member 106 may be based upon a
thrust caused compression of the elastomeric spring member 108 of
0.010 to 0.015 inch in either direction from the center position
shown in FIG. 2. And to withstand typical maximum thrust loads of
about 1,000 pounds, the spring rate required of the elastomer at
maximum deflection would be only about 66,000 to 100,000 pounds per
inch. In contrast, the spring rate of a single skirt member would
be about 0.5 to 1.0 million pounds per inch. The difference between
the elastomerically mounted outer skirt and a conventional single
skirt is even more pronounced when considering that the spring rate
during the first 0.001 inch of motion could be as low as 1,000
pounds per inch with this skirt and elastomer sandwich
arrangement.
Furthermore, the outer skirt 106 can be made very thin in
comparison with the inner skirt so that it can easily deform to the
cylindrical shape giving better bearing contact than the normal
single skirt. Preferably the outer skirt is tin plated or malleable
plated iron while the inner skirt may be made of aluminum for
lightness as compared with the common practice of normally forming
it from cast iron the same as the piston member. But it will be
appreciated that the primary purpose of elastomerically mounting
the outer skirt is to soften the blows of piston slap and thereby
reduce noise rather than provide sealing which is primarily left to
the oil rings which are still mounted in the lower portion of the
inner skirt.
However, elastomer is a relatively poor heat conductor and this
could result in an outer skirt temperature substantially higher
than that in a single skirt design. But this is prevented by the
expansible oil chambers 114 which provide for cooling of the outer
skirt and also provide a damping effect to further reduce the
piston slap noise as will now be described. With the forced oil
feed to the undercrown cavity of the piston assembly some of this
oil flows through the large orifices 116 into the top of the
expansible oil chambers 114 and then out through the smaller
orifices 118 in the bottom thereof after thus having traveled
substantially the length and area of the elastomeric member 108 in
the thrust regions of the outer skirt. This oil flowing through the
chambers 114 acts as a cooling medium within the elastomer and
between the two skirts and effectively carries away the heat of the
outer skirt to prevent it from developing excessive temperatures,
the smaller orifices acting to retard this coolant flow and
maintain the chambers substantially continuously full of the
cooling oil. For increased cooling, it will be understood that the
voids 112 in the elastomer could be extended radially outwardly so
that the inner surface of the outer skirt 106 then forms the outer
wall of the expansible chambers. In that case, the cooling oil
would then have direct contact with the outer skirt that it is
cooling. Furthermore, on radial thrust load impacts which cause the
noise, the chambers 114 will contract forcing oil out the orifices
116 and 118 and thus act as small shock-absorbers or dampers
thereby effecting further reduction in the piston-slap-caused
noise. In one actual construction which maintained low outer skirt
temperatures while substantially lowering the piston-slap-caused
noise, the large orifices 116 were drilled holes having a 1/8 inch
diameter and the small orifices were drilled holes having a 1/16
inch diameter. Of course, these sizes will vary with the usage.
The above described embodiment is illustrative of the invention
which may be modified within the scope of the appended claims.
* * * * *